A significant development of organometallic chemistry in recent years has been the increasing use of pentamethylcyclopentadienyl compounds. Not only are such compounds usually more soluble in organic solvents and more readily crystallized than their unsubstituted cyclopentadienyl analogs, but they are generally more stable as a result of the steric and electron-donation effects of the five methyl groups. This is particularly so for the (η5-pentamethylcyclopentadienyl)iridium complexes, where the η5-C5Me5 acts as an excellent ligand toward Ir(III) since it is displaced only with considerable difficulty.1 
Sheldrick's group in Germany has studied the biological activity of (η5-pentamethyl cyclopentadienyl)iridium complexes with polypyridyl ligands. Their work focuses on the intercalative binding properties of polypyridyl (pp) ligands (pp=dpq, dppz and dppn) into DNA. Recently they have showed that [(η5-C5Me5)IrCl(dppz)](CF3SO3) and [(η5-C5Me5)Ir((NMe2)2CS)(dppn)](CF3SO3)2 possess in vitro cytotoxic activity towards MCF-7 and HT-29 cancer cell lines, while [(η5-C5Me5)Ir(phen)Cl](CF3SO3) and [(η5-C5Me5) Ir(en)Cl](CF3SO3) are inactive against MCF-7 (breast cancer).2 Furthermore they have studied the influence of polypyridyl ligands (pp=dpq, dppz and dppn) and monodentate ligands (L=Cl, (NH2)2CS, (NMe2)2CS) on DNA intercalation (see FIG. 1).3 They also found that the complexes [IrCl3(DMSO)(pp)] (pp=phen, dpq, dppz, dppn), (FIG. 1), are potent cytotoxic agents toward the human cell lines MCF-7 and HT-29 and their IC50 values are dependent on the size of the polypyridyl ligands.4 Their work on iridium and rhodium polypyridyl complexes of general formula [Me(hal)3(sol)(pp)], in which hal is a halogenide and sol is a solvent, is described in EP2072521.
DNA binding of the type [(η5-C5Me5)Ir(Aa)(dppz)](CF3SO3)n containing S-coordinated amino acids has been studied and X-ray structure of [(η5-C5Me5)Ir(9-EtG)(phen)](CF3SO3)2 has been reported.5 
The biological activity of three novel indium(III) complexes with 1,2-naphthoquinone-1-oximato ligand are also described.6 The complex [(η5-C5Me5)Ir (pyTz)Cl]+ containing the 2-(pyridine-2-yl)thiazole (pyTz) N,N-chelating ligand is reported to be inactive towards human ovarian cancer cell lines A2780 and A2780cisR (cisplatin-resistant).7 